The present invention relates to a method and a device for diluted combustion.
Known from prior art are burners with flameless combustion. As described in the information sheet “projektinfo 07/06” of the BINE information service, which is available for download online at
http://www.bmwl.de/BMWi/Redaktion/PDF/B/bine-themeninfo-flammenlose-verbrennung,property=pdf,bereich=bmwi,sprache=de,rwb=true.pdf,
fuel gas and combustion air stream into a combustion chamber at a high flow rate in such burners. The major difference from conventional flame burners is the strong internal recirculation of exhaust gases in the combustion chamber, and their becoming mixed with the combustion air. The resultant diminished oxygen content in the combustion air and delayed mixture of air and fuel gas prevents the formation of a flame front. At high enough temperatures of at least 450° C. to 500° C., the fuel oxidizes in the entire combustion chamber volume. Very homogeneous temperatures set in as a result. The formation of thermal nitrogen oxides (NOx) that takes place predominantly at a flame limit is avoided. The more uniform temperature distribution not only causes the nitrogen oxide emissions to drop, but also allows a higher average combustion chamber temperature to be maintained.
In conventional burners, the combustion processes are most frequently monitored using UV measuring instruments. This is not always possible during flameless operation. As a rule, the useful space temperature is measured instead of measuring the UV signal. If a temperature limit is exceeded, ignition and complete burnout are ensured.
DE 44 00 831 A1 describes a burner with reduced corrosive gases. This burner encompasses a central feed channel for a primary oxygen stream, which is arranged on the center axis of a water-cooled feed channel for a fuel stream, and hence concentrically enveloped by the feed channel. The temperature of the primary oxygen stream is ≦30° C., and the percentage of primary oxygen stream in the stoichiometrically required oxygen quantity is <1%. Also provided is to recirculate combustion exhaust gases so as to ensure flameless combustion. For example, eight primary oxygen nozzles are provided, circularly enveloping the feed channel. Recirculating the combustion exhaust gases is intended to prevent temperature spikes in the flame root, and hence pollutant emissions. As a result, the flame is kept stable at the outlet, and burns at a low flame temperature. The cooling and associated low temperature of ≦30° C. of the primary oxygen stream yields a stable ignition flame with small quantities of primary oxygen, which produces a sufficient UV signal for monitoring the burner.
Known from U.S. Pat. No. 4,907,961 is an oxygen burner. This burner uses oxygen or oxygen-enriched air. In this burner, a first oxidant containing at least 30% v/v (volume per volume) oxygen is fed to a burner. This oxidant is supplied at a high speed. In addition, a second oxidant is to be supplied, the portion of which measures at least 1% of the total oxygen quantity fed to the combustion chamber. This second oxidant also contains at least 30% v/v oxygen, and is supplied at a low speed. For example, oxygen-enriched air can be generated by mixing pure oxygen and air. A stable flame is to be obtained at an interface between the gases.
U.S. Pat. No. 5,104,310 describes a burner that operates at a reduced flame temperature. This burner encompasses a central oxygen nozzle, and at least one nozzle for supplying the fuel, which concentrically envelops the oxygen nozzle. Provided radially spaced apart from the oxygen nozzle is at least one additional nozzle, which is designed as a de Laval nozzle. In this burner, the oxygen is supposed to be supplied at a very high rate, in particular to aspirate ambient air having a lower temperature than the flame before the oxygen from the oxygen nozzle reacts with the fuel. Several peripheral oxygen nozzles concentrically arranged around and spaced radially apart from the central oxygen nozzle can also be provided. The percentage of oxygen volume supplied through the peripheral nozzles measures between 60% and 90%, and preferably between 75% and 85% of the overall oxygen quantity fed to the burner. In this way, the majority of the oxygen-containing gas necessary for burning the fuel is supplied via the peripherally arranged oxygen nozzles. These oxygen streams aspirate additional ambient air before the oxygen reacts with the flame. The ambient air has a lower temperature than the flame. The aspiration of ambient air reduces the oxygen content and temperature in the peripheral oxygen streams. This mixture is prepared before it comes into contact with the fuel. This gas mixture consists of oxygen-enriched air, which contains at least 50% oxygen.
EP 0 685 683 A2 describes a burner with low NOx emission. In this burner, it can be provided that the combustion chamber be exposed by an air supply device to so high an air throughput that the combustion exhaust gases exiting the nozzle-like outlet of the combustion chamber become aspirated by the injector action, and are thereby again fed to the combustion air. After a temperature of 600° C. to 800° C. has been exceeded in the heating chamber, the fuel supply is to be switched over to bring this burner into a normal operating state, in which the high outlet pulse in particular of the combustion air from the combustion chamber is retained, largely suppressing the reaction of fuel and air in the area in front of the nozzle outlet into the combustion chamber and shifting it into the heating chamber. This burner can encompass a fuel nozzle enveloped by a coaxial fuel lance, wherein a combustion air feed pipe socket that empties into a combustion chamber is provided, which together with a combustion valve forms an air supply device.
Known from EP 1 355 111 A2 is a burner for flameless combustion. This burner encompasses a reaction chamber, which is fed with a fuel-gas mixture by a burner. The burner encompasses an air supply channel that extends until into an interior space enveloped by the burner head. A fuel pipe extends through the air supply channel until into the interior space. The fuel pipe is centrally arranged in the interior spaces, and hence enveloped by the air supply channel. The burner emits the fuel-air jet transversely to its longitudinal axis. An exhaust gas channel is arranged in or on the burner, concentrically or parallel to the longitudinal axis of the burner. The outlet direction of the burner and exhaust gas channel direction cross each other. In this burner, the fuel is introduced into the furnace chamber parallel or inclined relative to the furnace wall. The burner head is preferably configured in such a way that the fuel-air mixture assumes a high enough speed at the outlet opening to sweep away any flame. This permits a flameless mode of operation, in which the reaction between the fuel and air is distributed over a larger portion of the reaction chamber. In addition, the fuel-air jet aspirates a lot of hot exhaust gas, in particular in proximity to the inlet opening of the exhaust gas channel, and entrains the latter, additionally supporting flameless operation. For example, a recuperator or regenerator can be provided to preheat the fuel, air or fuel-air mixture. This burner is an air burner.